Electronic systems of higher sophistication conventionally are developed as one or a sequence of printed circuit boards which are retained within rack-mounted or stand-alone enclosures. These enclosures or housings typically include circuit supporting features such as backplane buses dedicated power supplies, cooling fans, and air filtering.
The electronics industry has recognized the advantages of establishing compatibility standards for the size, interconnect architecture, and mounting and insertion techniques associating these circuit boards, which are often referred to as "cards" or "modules", with backplane bus structures. To implement this call for standardization, industry organizations have evolved forms of consensus which has been manifested in the generation of guiding publications and the like. As an example, a back-plane bus having the trade designation "VERSABUS" was introduced by Motorola, Inc. to support the 16 bit microprocessor. European manufacturers proposed to modify this bus so that it could be used for systems constructed on standard Eurocard printed-circuit boards. Signetics/Philips, MOSTEK Corp., and Motorola, Inc. produced a draft standard for such a modified bus in 1981 which was named "VME Bus" (Versa Module Eurocard). For further discussion see, for example, "Micromputer Bus Structures and Bus Interface Design" by Dexter, Marcel Dekker, Inc., 1986, New York, N.Y. The VME architecture currently is widely utilized but is limited to 16 bit logic. As a consequence of this limitation, other standardizations have evolved or are under consideration, including a 32-bit logic future bus+and a 64-bit backplane.
Tracewell, U.S. Pat. No. 05,168,171 issued Dec. 1, 1992, describes an improved enclosure for circuit modules which is microprocessor driven to monitor the status of such voltage sources and provide outputs at a supervisory panel mounted at the front face of the enclosure. The enclosure further includes a computer monitored heat transfer air path of highly improved design. These monitoring features are powered from a separate power supply which, in turn, is buttressed by rechargeable battery back-up performing in conjunction with a d.c.-to-d.c. converter. With this form of enclosure, the somewhat costly circuit modules, for example ranging in value to about $10,000.00, are afforded substantially improved environmental and power input protection over their operational lifespans.
The design of these circuit modules or cards necessarily involves numerous phases or stagings. However, all such engineering endeavors culminate in the determination of requirements for power supply, heat removal capacities, and the like. The more final stages include the testing of modules, alone or in system configurations. This testing typically is carried out by adapting conventional enclosures or frame structures to the task. Where multiple cards are involved, somewhat complex wire wrapping typically is called for at the rear of the backplane. Such hand interconnecting, in turn, requires the identification of an interconnection or pin mount with myriads of backplane mounted pins, for example at the J2 regions of the backplane or the equivalents thereof. Very often, adjacently mounted power supplies severely interfere with this already physically arduous procedure. The probing of test points and the like at active faces of the cards while under test also calls for physical access. This access is provided by extender cards having one edge plugging into the cage backplane while the opposite end plugs into and supports the connecting end or edge of the card under test. As might be expected, the resultant card support is tenuous and somewhat structurally unsound. Where high speed data transfer is involved, the inherent circuit elongation may lead to inaccurate circuit evaluation.
The conventional approach to determining power supply requirements has involved a procedure of summing the published current requirements for each component of a card making up a system. A safety factor then is applied to that sum and the result so reached is specified as the power supply requirement. Often, this procedure results in an over-capacity of power supply with attendent costs, heat generation, and bulk packaging requirements. Alternately, current to the cards under test can be measured at the power supply. However, this involves the disassembly of the power supply distribution network for the purpose of accessing measurement points and the insertion of shunts and the like. Finally, a measurement of current is carried out. However, this practice may become so labor intensive as to be impractical.
The selection of fan requirements often is simply based upon prior experience, a size being selected by the engineer which assures more than adequate air flow. Alternately, where a heat analysis is called for, the fans within an enclosure adapted for testing can be disconnected from the enclosure power supply and driven at varying speeds from a controllable bench power supply. As this variation in fan speed is carried out, air temperatures can be measured using hot wire animometers, or the like, within the testing enclosure. Of course, the latter procedure is labor intensive and, consequently, costly. The use of experience based air flow determinations can be somewhat tenous during lengthy circuit "burn in" procedures where circuit heat generation may vary unexpectedly. Where such anomalies do occur, the opportunity for substantial financial loss increases considerably.
With the completion of testing of the hardware aspect for the circuit modules, very often the next procedure is to deliver the modules to programmers for the purpose of evolving complementary software or firmware. This calls for transporting the adapted enclosure with the modules to the working space of the programmer in addition to the bulksome and very often awkward assemblage of test frame and modules, the programmer often is confronted with open and accessible circuit components, for example at the power supply side of the backplane which may be hazardous to those inexperienced in working with circuits. Thus, the testing assemblages for the circuit modules need to be configured with the full panoply of technical participants in mind.